Alternating current welding transformer



April 5, 1960 H. L. M'ILLs ALTERNATING CURRENT WELDING TRANSFORMER 5 Sheets-Sheet 1 Filed April 18, 1957 95123 sul JEU www N. MNHN.

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ALTERNATING CURRENT WELDING TRANSFORMER Filed April 18, 1957 5 Sheets-Sheet 2 INVENTOR l/ENRY MIRE/vcr 141/41.: www MWL l:ou moon M mm. Y

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ALTERNATING CURRENT WELDING TRANSFORMER Filed April 18, 1957 5 Sheets-Sheet 3 INVENTOR.

' MEA/RY uuwcf l/LLS lrfoRA/er April 5, 1960 H. L MILLS 2,931,967

ALTERNATING CURRENT WELDING TRANSFORMER Filed April 18. 1957 5 Sheets-Sheet 4 INVENTOR. lle/Rv 4l/nwe: Mas

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4 fran/cr April 5, 1960 H. L'. MILLS ALTERNATING CURRENT WELDING TRANSFORMER Filed April 18, 1957 5 Sheets-Sheet 5 BYWW Arron/Ey United States Patent() ALTERNATING CURRENT WELDING TRANSFORMER Henry Laurence Mills, Excelsior, Minn. Application April 18, 1957, Serial No. 653,693 2 Claims. A(Cl. 323-51) j This invention relates to the art of arc Welders and more particularly to that segment of the art which has to do with alternating current arc welding transformers. Arc welding transformers heretofore available have usually been designed to use a ballast resistor in the secondary circuit so as to permit adequate stabilization of the arc during welding. Welding transformers for commercial service must be so constructed as to deliver a wide range of welding currents in the secondary ranging from as low as twenty amperes on up to two or three or four hundred amperes for heavy service. Some of the transformer designs have provided relatively high reactance so as to provide all or part of the ballast effect requisite to arc stabilization but such designs are unde- .sirable in other respects in that the transformer operates at low power factor and is unduly large, bulky, and requires excessive amounts of materials.

A further requirement for arc Welders is that regardlessrof the setting in respect to output amperage in the secondary second, it is desirable, when using certain kinds of welding rods particularly, to have a relatively high open circuit secondary voltage to assist in striking the arc. Welding transformers heretofore available while capable of providing such high open circuit voltage for certain welding current settings have nevertheless been deficient in this respect in that, at other secondary settings, the transformer welding apparatus failed to provide the desired high open circuit secondary voltage.

It is an object of the present invention to provide an improved arc welding transformer, and more particularly to provide an improved arc welding transformer capable of delivering a wide range of output currents in the secondary while at the same time being capable .of delivering a high open circuit voltage at the secondary ter- -minals for striking the arc. It is another object of the invention to provide an improved welding transformer apparatus of relatively light weight for the output of the machine and which is capable of operating at favorably high power factors throughout a large and effective range of welding current outputs of the machine. It is another object of the invent to provide an improved welding transformer circuit and system capable of affording the aforesaid results. Other and further objects ofthe invention are those inherent in the apparatus herein illustrated, described and claimed.

The invention is illustrated with reference to the drawings .in which:

Figure l is a simplified view of one form of the invention, this view being a side elevational view, as the apparatus is generally considered. In Figure l the circuits are shown schematically. Figure 2 is another view similar to that shown in Figure 1 and shows another `form of welding apparatus of the present invention.

Figure 2 is likewise a side elevational view partly in section and in it circuits are shown schematically. Figure 2,931,967 Patented Apr. 5, 1960y rangement of the present invention. In these figures, Figure 4 is a front elevational view of the welding transformer with the case partially broken away to show portions of the internal construction. Figure 5 is a horizontal sectional v-iew taken along the line and in the direction of arrows 5-5 of Figure l. Figure 6 is a vertical sectional view taken along the line and in the direction of arrows 6 6 of Figure 5. Figure 7 is a further horizontal sectional view taken along the line and in the direction of arrows 7-7 of Figure 6.

Referring to Figure 1 the apparatus of the present invention therein illustrated, partially in schematic form, comprises lan electro-mechanical arrangement wherein there is provided a main magnetic circuit generally designated 10 for the transformer. In its principal embodiment the magnetic circuit forms a rectangular frame in which at the left as shown in Figure l there is a vertical leg 11 which is connected by the horizontal top leg 12 to a right vertical leg 14 of the transformer which is in turn connected by the lower horizontal leg 15 to the bottom of the left leg 11. These four legs of the transformer main magnetic circuit 10 are in the shape of a rectangle which is higher than it is wide. It will be understood of course that the transformer may be placed so that the rectangular transformer core or magnetic circuit li) is arranged vertically as shown in Figure l, or it may be placed in any position desired such as with its major dimension horizontal. The rectangular magnetic core 1t) has at approximately the center position a shunting magnetic circuit composed of the leg 16 which is connected at 17 to the left leg 11 and a piece 30 attached to the primary coil mechanism 20. The leg 16 preferably terminates at a beveled surface 18.

The entire core 10-16-30 is made up of thin sheets of transformer core stock such as silicon steel. The thin sheets are cut in rectangular pieces and are stacked one on top of the other in the usual overlapping manner at the corners until the requisite thickness of dimension is provided. At the junction 17 between the shunting leg 16 and the leg 11 the shunting leg is preferably connected by running some of the laminations entirely through to f f the edge 11A with some of the laminations being stopped at the edge 11B. In this way there is interweaving of the, laminations of the leg 16 and 11 so as to form a strong mechanical joint. Also in laying the laminations forming the legs 11, 12, 14 and 15 overlapping is made in alternate directions at the corners on successive laminations so as to form a strong mechanical arrangement.

The leg 14 serves not only as a magnetic circuit for the transformer but also as a mechanical support upon which the primary structure generally designated 20 is adapted to move up and down. The laminations in the leg 14 extend from the upper leg 12 to the lower leg 15. The laminations are of course fastened together by bolts or clamps in any suitable clamping arrangement and thus form a strong support having a cross section which is rectangular. The surfaces 14A and 14B of the leg 18 are actually composed of the edges of the laminations and since the laminations may not be precisely accurate dimensionally or otherwise smoothed off, they will form a slight ridge extending all the way from the top to the bottom on surfaces 14A and 14B. The laminations are preferably stacked as evenly as possible and unless some of the laminations project excessively they need not be smoothed off.

The leg 14 is, in effect, a rectangular post, and advantage is taken of this by using it as a vertical slide upon which mechanical slider blocks 21 at the top and 22 at the bottom are mounted. These are fastened together by bolts, as shown in Figure 6 and they serve as a slider which mechanically slides on the leg 14 from an upper position as shown in full lines to a lower position. The

blocks 21 and'22 serve as a support for the primary winding-23 of the primaryv coil assemblyvv 20. Any suitable mechanical arrangement not illustrated may be used for holding the assembly 21, 22--23 together.

Connected to the assembly by means 'of a'thrust bearing-25 is the bottom end of the screw 26 which passes through-.the threaded block 27 on the frame 28. The upperend of the screw 26 is provided with a crankhandle at 29`by means of which it may be rotated in either direction. ylln this way the primary winding assembly 2l) may be adjusted up and down and in this manner the coil 23 may be moved to any selected position from the upper position shown in lfull lines to the lower position shown in dotted lines.

Upon thelower mechanical support 22 of the assembly 20 there is mounted the core'element 30 previously referred to; It is composed of a plurality of laminations ofttra'nsformer core steel stacked together and taken with theA leg 16 forms the shunting magnetic circuit. The laminations composing stack 30 are' mechanically supported frromthe lower frame member22 of the arrangement 2i). The laminations 30 are stacked so as to provide theV same thickness as the core, particularly core segment 16, of the shunting arrangement.v Also the core element 3d is provided with aV beveled surface at 31 which matches the beveled surface 18 of the core element 16. When the screw 26 is rotated so as to pull the primary arrangement 20 to its most elevated position the two beveled surfaces 1,8 an'd'31 are brought into close proximity so as to reduce the' reluctance of the shunt 16--3t). In this position the shunt has a maximum effectiveness. As the pri' mary` arrangement 20 is moved down, a greater air gap is provided in space 32y and this increases the reluctance Y of the shunt 16-'30 and reduces itsl magnetic shuntingV effect.V j

' y Lower down upon the leg 14 of the magnetic circuit there is mounted a secondary shown opposite the bracket 35. `The secondary 35 is composed of a lower pancake winding at 36 and an upper pancake winding at 37. These are both wound with spacings between turns and layers ,and are mechanically supported from the core 10 by structural means not shown. Itwill be noted that the two pancake windings 36 and 37 are separatedby a slightfspace which. enhances-ventilation and the degree of vertical spacing between windings permits some variation in reactance. The lower winding 36, which is designated Low O.C.V.`Coil, (for Low Open Circuit to be adjusted mechanically in relation to the second vcoilsf36` andl 37 which are'xedly supported: Fromthc' lines L1A and LZA leads 42 and 43 respectively extend to the coil 38, the line 43 being taken through the contacts 44A of the relay 44. The coil 44B of the relay 44 is connected to the lines 4S to terminal 46 on line N of the secondary output circuit and from terminals 47 on the secondary circuit LS the line 4S extends thru a manual control switch'49 to the relay coil 44B.

A simplified wiring diagram of the transformer arrangement is shown in Figure 3.

With reference to Figures l and 3, when thefprimary coil 20 is in the position shown in full lines in Figure 1, the shunt 16-30 is in a position such that the spacing 32 between the surfaces 18 and31 is a minimum, and hence the shunt has a maximum effectiveness, most of the magnetic flux produced by the primary 20 being thus shunted through a circuit composed of the upper portion of leg 11,- leg 12, the upper portion of leg 14 thence across the shunt Btl-16j. Depending upon the thickness of the air-'f gap 32 and the reluctance otherwise provided in thel shunting leg, some fraction of the magnetic ilux will continue down through the lower portion of the leg 14 hencevia legs 15 and the lower portions of leg ll'back contacts 44A,` and accordingly energizing the coil 38.

This coil 38 is connected so that its magnetomotive force isV in additive relationship to that of coil 23, and consef quently when a voltage across junctions 46 and 47 (which is'the same as acrossthe terminals G and L of the secondary output) is suilicient, coil 44B will be maintained`v energized and the primary booster coil 38 will continue to be energized. However when the secondary terminals` G and L'are connected to ltheir customary welding load the welding current flowing in the secondary circuit 36 will suicientlyr'educe the voltage across the terminals Grand L, (and hence also across the junctions 46 and 47),--so as toreduce the applied voltage upon coil 44B hasan internaljdiameter at surface 36A and anouter diameter at surface 36B. The winding 37 which is designated High O.C.V. Secondary Coil (for High Open Circuit Voltage), has an inner diameter at surface 37A and an outer diameter at surface37B. The more ele-Y vated position of coil 37 permits the induction therein of higheropen circuit voltages, when the primary coil 2t) is lowered to the position shown in dotted line, for lower (secondary ainperage), than occurs in coil 36 under the same conditions. Y

The coil 36 is connected by the lines LS and N to the terminals L and N respectively and the coil 37 is connected by the lines HS and N to the terminals H and N respectively. The terminal N may be regarded as neutral or ground Upon the leg 11 of the main magnetic circuit 10 and substantially opposite the lower secondary winding 36 there is mounted a Primary Boost Coil 38, which is mechanically supported from the core structure by bracing, not shown. p

. Primary supply voltage is provided by lines L1 and L2, the., supply being controlled by a push button Gn-Ot switch 39, which therefore controlsr the application of power to supply lines L1A and L2A of the transformer circuits. The lines L1A and L2A are connected by the flexible leads 40 and 41, respectively, to the coil 20 'of the primary, the tiexible leadsthus permitting the coil to an amount insuicient to maintain the relay 44 ener gized and it dropsrout thereby opening the contacts 44A thusde-energizing the coil 38. Accordingly by this arrangement a' relatively much higher open circuit volta-gre Y produced by theV coil 20.

`When'handle 29 is rotated appropriately coil 20 will be`- moved downwardly in the direction of arrow 51, the lowermostposition being shown in dotted lines Figure l. In'so moving,-the air gap 32 .between the faces 18 and 31 in theV shunting circuit is progressively increased and accordingly'at each successively lower position the proportion of magnetic ux which traverses the full magnetic circuit increases Vand the proportion which traverses the-shunting circuit 16-30 decreases. Also as the coil lgardlessiof whether the terminals rG and L are usedf i l however, the voltageacross the junctions 46 and 47`may be used as a control by means of which the operation ofthe primary kbooster coil 38 is controlled. The reafrom the coil 36, as when the welder has his ground and active electrode connected to terminals G and H respectively, still during the welding operation when welding current is flowing a voltage reduction occurs in the coil 36 eventhough no load is flowing through it, as compared to the voltage induced in such coil when no secondary current is being drawn from the coil 37.

Referring to Figure 2, the arrangement there shown is similar to that shown in Figure l except that the form of magnetic shunt which in Figure 1 is shown is composed of the components 16 and 30, in Figure 2 it is replaced by the shunt generally designated 55. Shunt 55 is composed of a stack 4of laminations having a length such that it is somewhat longer than the space between the inner surfaces 11B and 14A of the main magnetic circuit. The ends of the stack 55 of the laminations are beveled at surfaces 55A and 55B so as to contact respectively with the surfaces 14A of the main magnetic circuit leg 14 and the surface 11B of the'main magnetic circuit legr11. The entire stack of shunting laminations 55' is supported on a pivot at 60 mounted upon the suitable mechanical support 61 carried upon the magnetic circuit and the magnetic shunt is thus free to swing downwardly from the position shown in full lines to the position shown in dotted lines, in Figure A2. From the primary arrangement 20, which is movable up and down as Yshown by the arrows 51, there is a mechanical support 57 connected by a pivot 56 and a link 62 to a pivot 58 on the magnetic shunt 55. When the primary arrangement 20 is in its uppermost position as shown in Figure 2 the magnetic shunt 55 is swung upwardly until the' faces 55B and 55A contact respectively the faces 14AV and 11B of the main magnetic circuit thus making the shunt of maximum effectiveness. If desired air gaps may be provided at 55A and 55B by fastening pieces of material non-magnetic sheeting such the surfaces 14A and 55A and between the surfaces 11B and 55B. Such material, being of non-magnetic properties in effect introduces air gaps into the magnetic circuit of the shunt. As the primary winding arrangement 20 is lowered, by rotation ofthe screw 26, the shunt is swung down and it assumes some position such as shown in dotted lines. In the lowermost position the shunt 55 and the link 62 act as a stretcher suspension which determines the lowermost position to which the primary winding arrangement 20 can be lowered. Then as theprimary winding arrangement 20 is again elevated the link 62 will first push the shunt 55 in the direction of the arrow 64 until the 'linkage 62 is free again to swing upwardly and it then drawn the shunt 55 upwardly after which it is then elevated to the position as shown in full lines. In thisv way, variation in the shunting effect may be achieved, equivalent to that shown in Figure l.

Reference is now made to Figures 4-7 in which there is illustrated a preferred embodiment of the invention. In this illustration of the invention there is provided a sturdy sub-frame 100 which is preferably mounted upon an axle 101 having wheels 102 thereon. The wheels provide support at one side of the base frame and legs 103 are provided at another portion of the base frame, so as to provide stability. A handle 178 attached to the frame facilitates movement. Upon the frame there is a housing 105. The bottom of the frame is composed of expanded metal 106, and since the housing is raised up above the floor F by the wheels 102 and legs 103, ventilation is free to pass upwardly thru the entire housing, due to the chimney effect. The housing 105 is provided with louvers 106 at an upper portion, through which the Ventilating air may pass outwardly, and is provided with a ftop cover 107 attached by screws 10d-108 having a large central opening at 109 out of which the ventilating air may also pass. The core 10 of the welding transformer is supported inside of the housing on cross frames 112 of angle iron. In every instance the several 18,SQf which the core 10 is composed is made of two as rubber between Thus the laminations are stacked up so as to form for example two half-thickness core portions 11'-11' provided as shown in Figure 7 and fixed non-magnetic spacer blocks 115 are placed between the two half-thickness stacks. The same is true for all other portions of the main and shunting sections of the core. It will be noted from Fignlre 6 that the spacer 115-115 is not one continuous piece but is separate blocks throughout the vertical height of the transformer spaced from each other end-to-end to provide openings 11X11X thru which bolts --110 may conveniently be passed. In this way the laminations may be thought of as composed of two half-stacks separated from each other by the thickness of spacers with bolts 110 passing thru to the laminations and spacers stacked together. Of course, for all legs of the core composed of laminations, there may beprovided sturdy angles, as for example the angle 112 at the base which extends all the way across the transformer and connects directly to the frame, and constitutes a part of the frame. Similar clamping angles may be used as desired. The separated and spaced halfstacks thus provided at 11-11, 12-12, and 15-15 are in every instance composed of two separate stacks separated vapart from each other.

In the instance of the legs 11, 12, and 15 the spacing apart is accomplished by the spacers 11s, 12s and 15s but in the instance of the leg 14 of the transformer the two portions 14-14 as shown in Figure 7 are held apart in another manner. Thus in the case of these stacks of laminations, there is provided for each stack a sheet metal angle 114-114 which also are composed of sheet steel. These angles are composed of the flanges 114A and 114B which overlap respectively the adjacent lamination adjacent space 115 (which inother legs of the core 10 is filled with the spacers). The outer anges 114B seat against the edge face 14B of the stack of laminations. Angles 114-114 and the laminations of each portion of leg 14 against which the angles are placed are bolted in place between the bolts 115. The sheet metal angles 114A-114B can extend all the way up the top leg 12 of the core and down to the bottom leg 15 of the core. The metal angles serve to dene a space 115 between them, in which the frame work pieces 21 and 22 (which support the primary arrangement 20), are adapted to operate up and down.

It will be noted that the heads of the bolts v115 are attened so as to provide a maximum amount of space l 115 thus to permit the frame work pieces 21 and 22 to operate freely.

Referring to Figures 6 and 7 particularly the upper framework piece 21 has an interior portion 21A which reaches across in the space 115. This framework 21 has corners at 21C and 21D which serve as seats upon which insulation is provided for seating the upper end of the primary winding 23. Similarly, the framework 22 has a portion 22A which reaches across between the space 115 and likewise is provided with the corners 22C and 22D in which the insulation 122-123 is provided for supporting the lower end of winding 23. A plurality of bolts are provided at 124 which reach through portions 21A of the upper frame piece 21 and the portion 22A of the lower frame piece 22. When these bolts are tightened down the winding 23 is solidly supported by end pressure between the two frame pieces 21 and 22. The upper and lower frame pieces 21 and 22 are apertured to receive a screw 26. The upper piece 21 is provided with an aperture at 21E which is suflicient to permit the upper threaded Unthreaded end 26 of the screwv rod to pass completely therethrough with clearance. The `lower frame piece 22 is threaded at 22E to receive lowerV threaded end of the rod 26. The lowermost end of the rod 26 is turned down to a reduced diameter and is seated in a bushing 125 which is held in one of the spac- Yout under thev rim ofv the pan;

gangster thefbolts 110 which are lprovided at" intervals for holding-'f then lamin'nations clamped togetheril the top of the Ian-ma'gnetocircuit there are provided a pair of clamp# for a cross bearing plate 128 which is held in'place by the bolts 1-29-129, which fasten to the angles. Centrally of cross plate. 128 there is provided a bearing 130`which is of the thrust type, in which the upper end of the rod l 126y is journaled. At theupper end? of the-rod there is" provided a crank 29 covered by a' pan 29A and a` handle 29B. -The pan is of sufficient diameter so as to cover the" aperture 109 but is spaced vertically therefrom so that air can ow up through .the apertureV 109 and thence Whenever the handle 29B= isV turned'the'rod 26 will be turned and due to the screw threaded engagement with the lower frame piece member 22,the rodv will accordingly raise Aoi' lower the entire primary arrangement structure 20.

'Extending outwardly from the cross frame'member 128 Vis a bearing rod 132 (see Figures 4 and 5) having journaled at its outer end upon which'an indicator quadrant 13S- is swung, said'quadrant being provided with a cam'` edge at13'3A This quadrant 133 carries Vapointer at l33B which extends out through an arcuate slot in the frontofhousing 105 so as tov be in proximity with a scale uponwhich the welding aperturesk are parted.r The primary arrangement has a rod 134 extending out'from the lupper frame member 21 as shown in Figures 4 and 5.

Rod 134 is adapted Yto ride against the edge 133A of theV cam plate 133 and cause it to vbe rotated more or Vless depending upon thever'tical elevation of the primary arrangement'20. In Vthis way an indication is given on the front ofthe case' which shows the vertical elevation of theiprimary'arrangement 20, and the scale S is calibrated in welding amperages.' Y e A smooth sliding movement of the main arrangement 20 up and down on the'core portion 14-14-114-114 is achieved byrneans of the following arrangement: Referring to Figures 6 and 7 it will be noted-that from the lowerbracket 21 there Vis'a downwardly extending ear 22E through which there is threaded a screw 140 which is locked in place by lock nut 141. The screw bears 150) is provided. Y i AThe 'adjustment' of the screw 140 thus applying pres? lagainsta cross plate,142, and' this cross plate is provided Aat itsfouter ends,..se'e Figure 7, with a pair of bearin'g'pads 144-144. These bearing pads are preferably faced with a plastic facing such as Teon 145-145 the" pad and plastic being held in place by a screw as shown.

By adjusting the's'crew 140y more or less pressure can b eV placed upon the cross plate 142 and hence more or less pressure can be exerted by the Ypads 144 against the bearing-Hangings 144B and 114B of the angles which en-Y casel the outer edge faces of the laminations.

Alsoon the inside of the core, thelower frame piece 21 has'a downwardly extending ear at 21F which serves as. mountingy upon which apiece of tough plastic facing 1570 of Teon or the like is attached. 1t will be noted from Figure 7, that the plastic layer generally designated 150 has portions 150A-150 which seat directly against the edges 14A ofjthe laminations. i Theplastic is bentatrthe corners 150B-150B and extends to the left ask shown in Figure 7 to corners 150G-150C and then straight'across inrcontact with the ear 22F. A small channel 160 held in place by a* plurality of more screwsY 161 clamps the plastic in place. The plastic sheet is thusr very securely held and extends out and forms abearing between the ,edges of the'larninations in the half-stacks `30-30 (of the shunting circuit) and the adjacent lami-l with thethicknessv of the plastic' layer 150 forming in effect; au air gap inV theshunting circuit`116-30.' Thus Vvariation in heating of the winding. v

even through thespace 32 is-'quite'closed atv the'bejveled faces 18 and 31 a small andcarefully 'controlled '.gapfiiij the'mag'netic circuit (equal to the vthickness of the plastic'k sure uponthe cross plate 142 and hence upon the` pads v144 clamps the two portions 30 of the shunting' circuit flatly against the plastic layers A-150A and whichv ride upon the face 14A composed of the edges of the laminations of the core 14. The laminations may cause" ment 20 the upper frame member 21 is likewise provided'l kwith an" upstanding lug 21E whichis provided with a" similar'screw 160 having lock nut 161 which bearsV upon" the crossplate 162 which in turn pressesthe pads 164' againstr theY outer faces of` ank flanges 114B-,114B ofi.` the core'A structure.;l The inner upstanding bracketl 21Fv on the upper framework`21vbears againstra crossbar 165 which isjprovided with at each of its opposite'ends *with a Lpadl 166 similar to those at 164. Thus by adjusting A'the screw 160' the'pad 166 vbearing against the inner face 14A"fojf the 'laminations and pads 164 bearing against' the outer ianges 14B of the lamination structure can bei brought into carefully regulated pressure engagement with, 'the lamination structure and thus the upper portion of the primary structure 20 is stabilized against the vibration- In this way the entire primary arrange?, ment is very adequately supported upon the leg 14-14 or wobbling.

of the'core structure 10 and this can be done without any substantial vibration being exhibited. This is a considerable advantage because it permits wide latitude in adv-m justment of the position of the primary' 20v without` noticeable vibration or humming.

The support of the secondary coils 36-37 through bolts 172 extend upwardly through spacings between the lturns of the secondary coils and across the;

topof the upper secondary coil 37 or laid on the angles 173-173 through which the upper end of the `bolts 172 extend; Preferably springs are provided at 175-175y abouttheV upper protruding ends ofthe bolt and the spring is held down by the nuts -176. In this way a constant pressure is maintainedupon the windings 36-37 leven though there may be some change in dimension due `As many changes may be made in the illustrated constructions and many apparently widely different-embodiments of the inventionmay be made without departing? from the spirit and'scope thereof, it is intended that all matter contained in the above description or shownin the accompanying drawings shall be interpreted as illustrativeY and not in a limitingsense.

What I claim is: Y 1. A welding transformer comprising` a closed loop core of magnetically permeable metal having a straight section, a secondary coil encircling said straight section'A and iixedly located at one position of the length thereof and a mechanical support mounted on said straight section for translatory movement, a-main primary coil encirclingy said nstra-ight section and mounted on the mechanicalf support so as to be'movable vtherewithl toward and away' from a position proximate said secondary coil, a 'supple-j mental primary coil encircling a portion of the magnetic circuit 1mounted closely adjacent the secondary coil, said supplemental primary coil being connected so as to*Y producea magnetomotive'force produced by the additivey in respectv to the magnetomotive force produced by the"1 said main' primary coil and a voltage responsive circuiti' controllerconnectedin the circuit ofthe supplemental""l primary coil for controlling thev application-*ot pow'ef* is .upon insulating cross blocks -170 under the lower-coil"AV t 3.y Spacer cross blocks are provided at 171-171 and thereto, said voltage responsive circuit controllerbeing connected to the secondary coiloutlet so as to be responsive to the output voltage thereof and so as to close the circuit to the supplemental primary when the sec ondary coil voltage reaches substantially open circuit terminal voltage.

2. A welding transformer comprising a closed loop core of magnetically permeable metal having a straight section and a remote return section forming a closed loop with said straight section, said straight section being sufficiently rigid mechanically to form a post slide, a secondary coil encircling said straight section and Xedly mounted near one end of said straight section, a slide frame mounted for sliding movement on said straight section, a main primary coil mounted on the slide frame in a position so as to be movable toward and from a position proximate the secondary coil when the frame slides on the straight section, a shunt forming a shunt path extending from the remote return section to the straight section, said shunt being composed of at least two shunt portions of magnetic material serially connected, at least one of the shunt portions being mechanically supported on the slide frame and located so as to be proximate another of said shunt portions so as to form a shunt path of minimum magnetic reluctance when the frame is moved on the straight section for positioning the main primary coil remotely in respect to the secondary coil, and to space said shunt portion when the frame is moved on said straight section for positioning the main primary coil proximally said secondary coil, a supplemental primary coil encircling a portion of the magnetic core forming the magnetic circuit through the secondary coil and the shunt, said supplemental primary coil being connected in additive relation in respect to said main primary coil, and circuit control means connected in the circuit of said supplemental primary coil and connected to the output of the secondary coil so as to be responsive to the output voltage thereof for closing the circuit to the supplemental primary coil when the output voltage of the secondary coil approximates open circuit voltage for opening the circuit of the supplemental primary coil when the output voltage of the secondary coil is lowered by flow of welding current therethrough.

References Cited in the file of this patent UNITED STATES PATENTS 1,368,507 Kjekstad Feb. 15, 1921 2,471,222 Lorant May 24, 1949 2,475,044 Mulder July 5, 1949 2,572,455 Dunn Oct. 23, 1951 2,597,689 Welch May 20, 1952 UNITED -sTATEs PATENT OEFICE CERTIFICATE OE CORRECTION Patent No. 2,931,967 April 5 1960 Henry' Laurence Mills It is l hereby Certified that error-' appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as Corrected below.

v24,y for `"l'aminnationy lread laminations Column 8,y line l, for through read though 3 line 50v for V"winding".

Signed and sealed this 13th lday of 5September 1960.

(SEAL) Attest:

KARL AXLINE ROBERT C. WATSON Attest'1n8'-,off1c?r I Comiasoner of Pntents UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 931,967 April 5g 1960 Henry Laurence Mills It is hereby Certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as cerrected below Column 1v line 55g lfon Mnvent" read invention Column 5, line 49? for drawn read -edraws column 7Y line 2f for "'laminnations'read m lamnations 5 Column 8,; line t Y Signed and sealed this 13th vClay of September 1960.,

(SEAL) Attest:

RQBERT C. WATSON Attestng-.Offcer Commissioner of Patents 

